The invention relates, generally, to devices for winding webs of material and, more particularly, to an improved wound roll vibration detection system.
Winding machines are used in the paper industry for winding webs of paper to and from rolls. Referring to FIG. 1, a typical prior art paper winding machine is indicated in general at 10. The winding machine contains an unwinding roll 14 from which a paper web 16 is unwound. The paper is fed through the winding machine 10 onto wound roll 18 resting on drums 20 and 21 for supporting the wound roll 18. As wound roll 18 rotates, the paper accumulates onto the roll, and the roll""s diameter grows. However, the rotation of wound roll 18 also results in undesirable vibration of the roll.
A rider roll 30 contacts the outer surface of wound roll 18 to steady the wound roll against excessive vibration. At higher rotational speeds, however, the wound roll begins vibrating at increasingly higher magnitudes. Rider roll 30, due to its contact with wound roll 18, thus also vibrates, causing rider roll 30 to lift off of wound roll 18 and lose contact with the wound roll. The still vibrating wound roll 18 then is free to oscillate on drums 20 and 21. This oscillation can produce mechanical wear of the winding equipment, and may even result in wound roll 18 being displaced from drums 20 and 21 entirely, a phenomenon known as xe2x80x9croll kick out.xe2x80x9d To prevent such occurrences, it is common to employ vibration detection systems to attempt to detect, and limit, the excessive vibration caused by rotation of the wound roll.
As illustrated in FIG. 1, prior attempts to reduce excessive vibration of the wound roll 18 have included measuring the vibration of the rider roll 30 with an instrument such as an accelerometer 46. Typically this vibration signal is read by a detector 48, which is in communication with the drive system 52 of the winding machine and is configured to reduce or even cease the motion of winding machine 10 if vibrations are detected above a certain level. A problem with such prior art systems, however, is that some components of the vibration of the wound roll 18 are caused by sources other than the roll""s rotation, such as DC offset, background noise or peripheral vibrations. As a result, the vibration level detector 48 erroneously detects indications of excessive vibration, and thus the drive system 52 of the winding machine 10 is decelerated or halted unnecessarily, resulting in undesirable down time, slower winding times and inefficient performance.
Prior art devices have attempted to control the vibration of the wound roll while reducing unnecessary deceleration or down time in various ways. For example, U.S. Pat. No. 5,909,855 to Jorkama et al. discloses a paper winding method whereby accelerometers measure the vibration of the wound roll or take-up roller of a paper winding machine. As a result, frequency ranges of excessive vibrations may be predetermined by test runs during which the take-up roller is run at various frequencies. During the actual winding operation, when the rotational frequency reaches particular values previously determined to produce excessive vibrations, the running speed of the winding machine is dropped until the rotational frequency of the take-up roller is safely below these frequencies.
A disadvantage of the method and system of the Jorkama et al. xe2x80x2855 patent, however, is that the predetermined frequency ranges of excessive vibrations may become inaccurate if the vibration characteristics of the paper being wound changes. Because the method and system cannot detect such changes, the rotational frequency that causes excessive vibrations may not be successfully avoided. Furthermore, performing preliminary test runs is an inefficient use of time and other resources.
Prior art devices have also used band pass filters and Fast Fourier Transforms to detect winding machine vibrations. For example, U.S. Pat. No. 5,679,900 to Smulders discloses a system for detecting defects in vibrating or rotating paper machinery. The system includes an accelerometer that sends a vibration signal through a band pass filter selected from among several filters. Each filter is set at a different predetermined range of frequencies. The user selects in advance one or more band pass filters according to a desired frequency band, a speed range of winding machinery, or an analyzing range. An envelope detector shapes and enhances the filtered signals before they are subjected to a Fast Fourier Transform (FFT) analysis. While the Smulders xe2x80x2900 patent presents an analysis tool, it does not teach how the results provided thereby may be utilized to control the machinery to prevent excessive vibrations from occurring. In addition, the Smulders xe2x80x2900 patent requires that the user manually select the desired band pass filter, and thus the desired passband.
Accordingly, it is an object of the present invention to provide a vibration detection system that automatically adjusts the winding speed of a machine to avoid intense vibrations of the wound roll due to its rotational speed.
It is a further object of the present invention to provide a vibration detection system whereby the component of wound roll vibration attributable to the rotational speed of the wound roll may be determined so that the winding speed of the winding machine is not unnecessarily decreased.
It is a further object of the present invention to provide a vibration detection system that may be easily installed on existing winding machines.
It is still a further object of the present invention to provide a vibration detection system that provides a low computational burden for the system controller.
The present invention is a system that provides inputs of a winding machine""s wound roll vibration, line speed and wound roll diameter to a programmable controller. The programmable controller uses the line speed and diameter feedback to calculate the rotational frequency of the wound roll as it rotates and accumulates paper. In a first embodiment of the invention, the calculated rotational frequency is used by the programmable controller to select a passband for a band pass filter. By filtering the vibration feedback through the band pass filter, the portion of the vibration of the wound roll not attributable to its rotation is attenuated. A level detector is then used to detect the amplitude of the filtered vibration feedback, that is, the portion of the vibration that is attributable to the rotation of the wound roll. If the detected vibration amplitude exceeds a predetermined level, a signal is sent to the winding machine drive system so that the winding machine is shut down or, alternatively, decelerated until the detected vibration signal is below the predetermined level whereat the wound roll may rotate without experiencing intense vibrations.
In a second embodiment of the invention, a Fast Fourier Transform analysis is performed on the vibration feedback so that a table of vibration amplitudes vs. frequencies is produced. The calculated wound roll rotational frequency is then used to select from the table the amplitude of the vibration at the rotational frequency of the wound roll. This amplitude is compared to a predetermined level in a level detector and, as with the first embodiment, the winding speed of the winding machine is decreased if the predetermined level is exceeded.